1 / 25

ECE 436a Networking: Principles, Protocols, and Architectures

ECE 436a Networking: Principles, Protocols, and Architectures. Wireless and Mobile Networks Part 2 November 25, 2008 Department of Electrical and Computer Engineering University of Western Ontario. no mobility. high mobility. What is mobility?.

meira
Download Presentation

ECE 436a Networking: Principles, Protocols, and Architectures

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. ECE 436aNetworking: Principles, Protocols, and Architectures Wireless and Mobile Networks Part 2 November 25, 2008 Department of Electrical and Computer Engineering University of Western Ontario

  2. no mobility high mobility What is mobility? • spectrum of mobility, from thenetwork perspective: mobile wireless user, using same access point mobile user, passing through multiple access point while maintaining ongoing connections (like cell phone) mobile user, connecting/ disconnecting from network using DHCP.

  3. Mobility: Vocabulary home network: permanent “home” of mobile (e.g., 128.119.40/24) home agent: entity that will perform mobility functions on behalf of mobile, when mobile is remote wide area network Permanent address: address in home network, can always be used to reach mobile e.g., 128.119.40.186 correspondent

  4. Mobility: more vocabulary visited network: network in which mobile currently resides (e.g., 79.129.13/24) Permanent address: remains constant (e.g., 128.119.40.186) Care-of-address: address in visited network. (e.g., 79,129.13.2) wide area network home agent: entity in visited network that performs mobility functions on behalf of mobile. correspondent: wants to communicate with mobile

  5. How do you contact a mobile friend: • search all phone books? • call her parents? • expect her to let you know where he/she is? I wonder where Alice moved to? Consider friend frequently changing addresses, how do you find her?

  6. Mobility: approaches • Let routing handle it: routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange. • routing tables indicate where each mobile located • no changes to end-systems • Let end-systems handle it: • indirect routing: communication from correspondent to mobile goes through home agent, then forwarded to remote • direct routing: correspondent gets foreign address of mobile, sends directly to mobile

  7. Mobility: approaches • Let routing handle it: routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange. • routing tables indicate where each mobile located • no changes to end-systems • let end-systems handle it: • indirect routing: communication from correspondent to mobile goes through home agent, then forwarded to remote • direct routing: correspondent gets foreign address of mobile, sends directly to mobile not scalable to millions of mobiles

  8. mobile contacts foreign agent on entering visited network foreign agent contacts home agent home: “this mobile is resident in my network” 1 2 Mobility: registration visited network home network End result: • Foreign agent knows about mobile • Home agent knows location of mobile wide area network

  9. foreign agent receives packets, forwards to mobile home agent intercepts packets, forwards to foreign agent correspondent addresses packets using home address of mobile mobile replies directly to correspondent 3 2 4 1 Mobility via Indirect Routing visited network home network wide area network

  10. Indirect Routing: comments • Mobile uses two addresses: • permanent address: used by correspondent (hence mobile location is transparent to correspondent) • care-of-address: used by home agent to forward datagrams to mobile • foreign agent functions may be done by mobile itself • triangle routing: correspondent-home-network-mobile • inefficient when correspondent, mobile are in same network

  11. Indirect Routing: moving between networks • suppose mobile user moves to another network • registers with new foreign agent • new foreign agent registers with home agent • home agent update care-of-address for mobile • packets continue to be forwarded to mobile (but with new care-of-address) • mobility, changing foreign networks transparent: on going connections can be maintained!

  12. foreign agent receives packets, forwards to mobile mobile replies directly to correspondent 4 2 4 1 3 Mobility via Direct Routing correspondent forwards to foreign agent visited network home network wide area network correspondent requests, receives foreign address of mobile

  13. Mobility via Direct Routing: comments • overcome triangle routing problem • non-transparent to correspondent: correspondent must get care-of-address from home agent • what if mobile changes visited network?

  14. 1 2 4 3 5 Accommodating mobility with direct routing • anchor foreign agent: FA in first visited network • data always routed first to anchor FA • when mobile moves: new FA arranges to have data forwarded from old FA (chaining) foreign net visited at session start anchor foreign agent wide area network new foreign network correspondent agent new foreign agent correspondent

  15. Mobile IP • RFC 3220 • has many features we’ve seen: • home agents, foreign agents, foreign-agent registration, care-of-addresses, encapsulation (packet-within-a-packet) • three components to standard: • indirect routing of datagrams • agent discovery • registration with home agent

  16. Mobile IP Mobile IP is best understood as the cooperation of three separable mechanisms: • Discovering the care-of address • Registering the care-of address • Tunneling to the care-of address

  17. Capabilities of Mobile IP • Discovery – mobile node uses discovery procedure to identify prospective home and foreign agents • Registration – mobile node uses an authentication registration procedure to inform home agent of its care-of address • Tunneling – used to forward IP datagrams from a home address to a care-of address

  18. Operation of Mobile IP • Mobile node is assigned to a particular network – home network • IP address on home network is static – home address • Mobile node can move to another network – foreign network • Mobile node registers with network node on foreign network – foreign agent • Mobile node gives care-of address to agent on home network – home agent

  19. foreign-agent-to-mobile packet packet sent by home agent to foreign agent: a packet within a packet dest: 128.119.40.186 dest: 128.119.40.186 dest: 128.119.40.186 packet sent by correspondent dest: 79.129.13.2 Mobile IP: indirect routing Permanent address: 128.119.40.186 Care-of address: 79.129.13.2

  20. Wireless, mobility: impact on higher layer protocols • logically, impact should be minimal … • best effort service model remains unchanged • TCP and UDP can (and do) run over wireless, mobile • … but performance-wise: • packet loss/delay due to bit-errors (discarded packets, delays for link-layer retransmissions), and handoff • TCP interprets loss as congestion, will decrease congestion window un-necessarily • delay impairments for real-time traffic • limited bandwidth of wireless links

  21. IP addresses: how to get one? • DHCP:Dynamic Host Configuration Protocol

  22. IP addresses: how to get one? Q: How does host get IP address? • hard-coded by system admin in a file • Wintel: control-panel->network->configuration->tcp/ip->properties • UNIX: /etc/rc.config • DHCP:Dynamic Host Configuration Protocol: dynamically get address from as server • “plug-and-play”

  23. DHCP: Dynamic Host Configuration Protocol Goal: allow host to dynamically obtain its IP address from network server when it joins network Can renew its lease on address in use Allows reuse of addresses (only hold address while connected an “on” Support for mobile users who want to join network (more shortly) DHCP overview: • host broadcasts “DHCP discover” msg • DHCP server responds with “DHCP offer” msg • host requests IP address: “DHCP request” msg • DHCP server sends address: “DHCP ack” msg

  24. E B A DHCP client-server scenario 223.1.2.1 DHCP 223.1.1.1 server 223.1.1.2 223.1.2.9 223.1.1.4 223.1.2.2 arriving DHCP client needs address in this network 223.1.1.3 223.1.3.27 223.1.3.2 223.1.3.1

  25. DHCP discover src : 0.0.0.0, 68 dest.: 255.255.255.255,67 yiaddr: 0.0.0.0 transaction ID: 654 DHCP client-server scenario arriving client DHCP server: 223.1.2.5 DHCP offer src: 223.1.2.5, 67 dest: 255.255.255.255, 68 yiaddrr: 223.1.2.4 transaction ID: 654 Lifetime: 3600 secs DHCP request src: 0.0.0.0, 68 dest:: 255.255.255.255, 67 yiaddrr: 223.1.2.4 transaction ID: 655 Lifetime: 3600 secs time DHCP ACK src: 223.1.2.5, 67 dest: 255.255.255.255, 68 yiaddrr: 223.1.2.4 transaction ID: 655 Lifetime: 3600 secs

More Related